1988 K100 Fuel Injectors won't squirt...

Just a guess, since you indicate none of them function, no electrical energy is getting to them. Is there a fuse to check, or can you measure for proper current at the injector caps? If nothing shows there, maybe track it back?

Make sure your ECU (computer) plug is clean and firmly plugged in. You can use a test light to see if the injectors are getting an electrical pulse. You can apply 12v directly to the injector to see if it clicks open. Suggest you attach a jumper to the injector and then touch the other end to the battery. Have an extinguisher handy in case of stray sparks.......

You might also pour a can of Sea Foam into the gas tank,,try to start it for a couple minutes, let it sit overnight and see if that cleans out the gas lines etc.

Definately Electrical...

There is plenty of clean fuel pressure at the rail so it must be electrical. The injectors fire fine if voltage is applied directly to them. All the fuses look fine. Tomorrow I am cleaning the central ground under the tank.

According to a troubleshooting document that I am reading there are 4 components that feed the injector computer.

1. Electronic Ignition Module
2. Airflow Meter
3. Idle Switch (which I think is the throttle positioning sensor).
4. Water temperature sensor.

I'll focus on these components first....

Thanks for the suggestions so far. I'll write more as I make progress with this bike.

When fuel sits for prolonged periods it turns to gummy glue. Since we know there was bad gas in the system, and the pump, filter, and lines were gummed up it is reasonable to believe that fuel in the injectors has also turned to glue and they are stuck. When the K100 bikes first came out this was very common even if bikes sat six months or a year. It is possible we are getting better gas now than in 1985 but I doubt it.

I think the injectors need to be taken to a professional shop that is equipped to back flow and clean injectors. They too may fail at the task but it is worth a try. If they fail then new injectors will be required.

If this was a running bike on which all 4 injectors quit at once I wouldn't believe it was the injectors unless they received a dose of water or other waste. But on a bike that was left parked for a long period I would think gummed-up injectors more likely that bad electronics.

Paul he said he swapped out injectors from a running bike. Electrical probably?

MindTrainer said:

There is plenty of clean fuel pressure at the rail so it must be electrical. The injectors fire fine if voltage is applied directly to them. All the fuses look fine. Tomorrow I am cleaning the central ground under the tank.

According to a troubleshooting document that I am reading there are 4 components that feed the injector computer.

1. Electronic Ignition Module
2. Airflow Meter
3. Idle Switch (which I think is the throttle positioning sensor).
4. Water temperature sensor.

I'll focus on these components first....

Thanks for the suggestions so far. I'll write more as I make progress with this bike.

Click to expand...

You missed one.. the Hall-Effect sensor tells the ECU (L-Jetronic, which never goes bad - about as bulletproof as is possible) to fire the injectors and ignition. Simple test - are the plugs firing? If so - the HES is working.

The airflow meter is very unlikely since the ECU pretty much ignores it when starting the bike (since no air is actually flowing through it - or not enough to matter)..

Idle position switch - possible, but never heard of one failing. Might be mal-adjusted. You can unplug it - and it's out of the circuit (and the bike will start/run just fine with it out of the circuit.)

Water temperature switch - also unlikely. One failing shouldn't stop ALL injection.

I'd suggest going to Harbor Freight and buying one of their little electrical trouble-probe lights made for 12V use. Either that or Radio Shack for a small digital voltmeter - either/both will be very handy in troubleshooting an early K bike.

What to test first?
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With the ignition ON - you should have 12VDC on one side of each injector (they are wired in parallel). The injectors are pulsed by switching the other side to ground via the L-Jetronic analog brain. First thing to look at - do you have 12V going to the injectors (if they aren't being switched - it will show on both sides of the injector when measured to ground..)

RESIST the impulse to randomly swap out anything that anyone mentions as a possible problem until we can narrow down where the problem is... doing that is called "flailing" (throwing parts at a problem), and while eventually it will probably fix the bike, it gets expensive getting to the fix.

So - check for volts at the injectors and let us know what'cha find. You can do the test with the electrical probe tester, or with a voltmeter.

IF you find voltage - then hook your probe-tester (or voltmeter) across the terminals going to one of the injectors (you can back-probe these connectors IF you're careful..) and crank the engine. Does the proble flash? (Or voltmeter show a pulsed voltage of 0-12V?)

Get back to us with the results and we can decide where to go from there..

The few times (yes, more than once) that the bikes have been in this state was caused by not having the ICU connection seated all the way. You really need to feel/hear that click when you insert and push that handle in.

Found it ! Bad wire...

I was taking Don's advise and found no voltage at the injectors at all at any time. Then while looking at all the connections again is when I spotted a flat area in the insulation on the engine wiring harness. It looks like it may have gotten pinched by the tank because it was miss routed up over the frame. My multimeter verified that it was an open circuit when disconnected.

I cut the wire, re soldered it and used 5 cents worth of heat shrink and she started right up.

Thanks everyone for being here with your good advise. It sure makes taking on a job a lot more fun.

Nice when it works out huh! If you have to return the injectors that are in it you might want to send your old ones off to Mr. Injector or someone similar. Enjoy your new find.

Glad to hear it was of help. Sometimes it really goes faster if we spend some time thinking it through a bit.

Good deal! Thanks also for letting us know how it worked out!